1. Field of the Invention
The present disclosure relates to an imaging apparatus, such as a video camera or a digital camera, that corrects a distortion in an image captured by using the rolling shutter method.
2. Description of the Related Art
In recent years, many video cameras and digital cameras have employed complementary metal-oxide semiconductor (CMOS) image sensors of the rolling shutter method. This type of image sensors has a problem in that, due to occurrence of a time lag among imaging time points of the respective lines, an image captured with a panning operation is diagonally distorted, an image captured with a tilting operation is extended or shrunk, an image captured with a camera shake shows an undulating distortion, and a captured image of a moving object is distorted.
Such a camera is often combined with sensor driving of the global shutter method or a mechanical shutter when capturing a still image, thereby eliminating the time lag among imaging time points. However, these methods cannot expose the image sensor to light and read out an image from the image sensor simultaneously so as to increase an interval between imaging operations, and therefore is not suitable for taking a moving image.
Some cameras, which capture a moving image by the rolling shutter method, store the captured image in a buffer memory and change a reading position of each line, thereby correcting distortion, as discussed in Japanese Patent Application Laid-Open No. 2006-186885. The reading position of each line is determined by detecting a movement amount of the camera relative to an object by using, for example, a gyro sensor.
For example, as illustrated in FIG. 11A, a captured image 1100 is diagonally distorted since it is captured while the camera is being panned to the left side, but can be output as a captured image 1110 with the distortion corrected by changing the reading position of each line with use of a detection result of a movement amount. The target object in the captured image 1100 is a landscape, and its distortion is effectively corrected.
However, according to the conventional correction method, if the camera moves by following a target object such as a running vehicle or person, correcting the image according to the movement of the camera results in a distortion of the target object image which is captured without being distorted in the original image, and an output of such an image.
For example, as illustrated in FIG. 11B, a captured image 1120 is an image captured following a person running to the left side while the camera is being panned. In this case, the distortion is corrected based on the movement of the camera, whereby the corrected image 1120 is output as an image 1130 in which the person is distorted in the opposite direction.
The target object in the captured image 1120 is the person. Therefore, the correction of the image that results in a distortion of the person portion in the image is not an appropriate correction, even though this correction can eliminate the distortion of the landscape portion in the image.